<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #box {
            width: 200px;
            height: 30px;
        }

        #dv {
            border: 1px solid #ff0000;
            display: none;
        }
    </style>
    <script type="text/javascript">
        window.onload = function () {
            var box = document.getElementById("box")
            var dv = document.getElementById("dv")
            box.onmouseenter = function () {
                dv.style.display = "block"
            }
            box.onmouseleave = function () {
                dv.style.display = "none"
            }
        }
    </script>
</head>
<body>
<div id="box">
    <input type="checkbox">未来两周记住密码
    <div id="dv">为了您的信息安全请不要再网吧 或者 公共电脑上使用</div>
</div>
</body>
</html>